Self-crosslinking aqueous dispersions

ABSTRACT

The present invention is directed to polymer compositions containing a vinyl polymer component (A), formed by polymerization of α,β-ethylenically unsaturated monomers, one which contains at least one hydroxyl group and one which contains no hydroxyl groups; a crosslinker component (B); an additive component (C); and a solvent component (D). The composition is useful for backcoating woven substrates and as a binder composition for non-woven substrates.

FIELD OF THE INVENTION

This invention relates to self-crosslinking polymer compositions. Theself-crosslinking polymers of the present invention are particularlyuseful as binders in backcoating textile or non-woven fabrics and asadhesives. When a substrate is coated or impregnated with theself-crosslinking polymers of the present invention the strength of thesubstrate is enhanced while its flexibility and softness are retained.

DESCRIPTION OF THE RELATED ART

It is known to those skilled in the art that hydroxyl containing vinylcopolymers may be crosslinked with crosslinking agents. U.S. Pat. No.3,208,963, discloses a method for forming a vinyl copolymer of vinylacetate and hydroxy alkyl acrylate. The vinyl polymer of the referenceis prepared in an organic solvent solution. The polymer of the referencemay further be crosslinked by a crosslinking agent or catalyst,comprising hydrochloric acid, glyoxal, dimethylol ethylene urea,dimethylol urea, trimethylol melamine, trimethylol phenol, andpara-toluene sulfonic acid.

U.S. Pat. No. 3,203,918, discloses a hydroxy acrylate-vinyl alcoholcopolymer prepared in an organic solvent solution and subsequentlyconverted into the form of an aqueous solution. Coatings or films aredeposited from their aqueous solutions and subsequently renderedinsoluble by aging, by application of heat and/or by prior formulationwith a crosslinking agent. Such crosslinking agents include aldehydessuch as glyoxal, and furfural aldehydes, urea type crosslinkers,melamine formaldehyde condensates, non-oxidizing inorganic acids,non-volatile organic acids, and acidic salts such as ferric chloride,chromic nitrate, etc.

U.S. Pat. No. 3,597,313, discloses a composition comprising awater-soluble polymer having a multiplicity of hydroxy substituents onthe polymer chain and this polymer is then modified with cyanamide torender it cationic. The polymer may be crosslinked with glyoxal, thecrosslinked thermosetting resin of the reference are then preferablyadsorbed on cellulose, paper-making fibers in an aqueous dispersion, andthe suspension is then formed into a wet-laid web, which improves thewet-strength of paper making products.

U.S. Pat. No. 4,652,603, discloses an adhesive composition comprisingvinylidene chloride, a polar monomer having one or more hydroxyl groupsand, optionally, a plasticizing monomer for vinylidene chloride incombination with a crosslinking agent for the hydroxyl group; thecomposition of the reference may be crosslinked with glyoxal. Suchadhesive compositions are useful for laminating hydrophobic films, tonon-hydrophobic films or other hydrophobic films or substrates so as toprovide laminated structures having good oxygen and moisture vapor paperproperties.

U.S. Pat. No. 5,116,890, discloses a non-formaldehyde, self-crosslinkinglatex which upon drying and curing provides a film having good tensile,elongation, water resistance and antiwicking properties. The latex isprepared by reacting in aqueous suspension or slurry of a starch-polymergraft with a glyoxal compound. The latex of the reference provides asystem which is compatible with an acrylic latex and provides anon-formaldehyde self-crosslinking resin with tensile strengthequivalent to an all acrylic binder system, but exhibiting lesselongation and good water resistance.

U.S. Pat. No. 4,695,606, discloses a coating binder additiveencompassing a blocked glyoxal resin mixed with a vinyl or acrylic watersoluble polymer which is reactive with free glyoxal. Thus, the glyoxalresin component of the reference is blocked to inhibit it from reactingwith the other components of the paper coating composition prior tocuring. The curing process unblocks the glyoxal and the resin allowingthem to react with the binder and polymer resulting in a crosslinkedbinder with superior strength and improve printing properties.

U.S. Pat. No. 5,179,150, refers to an improved creping compositioncomprising glyoxylated vinyl amide polymers in combination withpolyvinyl alcohol. The glyoxylated-vinyl amide and the polyvinyl alcoholcompositions of the reference are used in a mixture in applications forpaper manufacture.

It is well known to those skilled in the art that crosslinking a polymerresults in increased strength and glass transition temperature (Tg) ofthe polymer; and that crosslinking also decreases solubility andincreases hardness and stiffness of the polymer. Soft polymeric bindersof low Tg are relatively weak, while polymeric materials of high Tgprovide backcoated fabrics that are stiff and esthetically unpleasant.

There exists a need for self-crosslinking polymer compositions whichprovide a substrate with strength, good draping, flexibility andpleasing feeling.

There also exists a need for a method to treat substrates with polymercompositions in order to enhance the strength of the substrate whileproviding additional properties such as good draping, flexibility, andpleasing feeling to touch.

SUMMARY OF THE INVENTION

Applicants have discovered novel self-crosslinking polymer compositionsand a novel method for treating substrates with these self-crosslinkingpolymer compositions. A substrate, after treatment with theself-crosslinking polymer compositions of the present invention,exhibits the combined properties of strength, softness and flexibility.It would be expected that crosslinking of a polymer decreasessolubility, increases strength, and decreases softness and flexibility.Crosslinking of a polymer is normally associated with increasedtoughness and brittleness. The discovery that a self-crosslinkingpolymer, when applied as a binder on a substrate, provides the substratewith combined softness, flexibility and strength is both unexpected anddesirable.

It is an object of the present invention to provide self-crosslinkingpolymer compositions which are stable when stored as a one-packagesystem and are suitable for use in backcoating formulations applied tovarious substrates.

It is another object of the present invention to provide a method oftreating substrates with self-crosslinking polymer compositions and toprovide those substrates with a combination of softness and strengthproperties.

It is a further object to provide self-crosslinking polymer compositionswhich are able to crosslink without the use of toxic reagents; and whichcrosslink, optionally, without added catalyst or heat.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts the change in elongation of a polymer of the presentinvention compared to commercial polymer materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides self-crosslinking polymer compositionsuseful as textile backcoating formulations and having other textileapplications. The polymer compositions encompass: (A) a vinyl polymercomponent, present in an amount of from 20 to 65 weight percent, basedon the total amount of the polymer composition. The vinyl polymer isformed by copolymerizing: (a) at least one first α,β-ethylenicallyunsaturated monomer which contains at least one hydroxyl group, presentin an amount from 2.0 to 25.0 weight percent based on the total amountof copolymerizable monomers; and (b) a second α,β-ethylenicallyunsaturated monomer which contains no hydroxyl groups, present in anamount from 75.0 to 98.0 weight percent, based on the total amount ofcopolymerizable monomers. The second α,β-ethylenically unsaturatedmonomer preferably contains: (i) an alkyl (meth)acrylate ester, and mayinclude (ii) optionally, a styrenic monomer, (iii) optionally, a(meth)-acrylamide monomer, (iv) optionally, a (meth)-acrylonitrilemonomer, (v) optionally, an additional copolymerizable monomer, and (vi)optionally, a copolymerizable crosslinkable monomer.

Further, the polymer composition contains (B) a crosslinker component,present in an amount of from 0.1 to 15.0 weight percent based on thetotal amount of component (A). In addition, the polymer composition maycontain (C) an optional additive component, present in an amount of upto 2.0 weight percent, based on the total amount of component (A); and(D) a solvent component being the remainder of the polymer composition.

COMPONENT (A)--Vinyl Polymer

Vinyl polymers in accordance with the present invention are thepolymerization product of the following monomers:

Component (a)

Component (a) contains at least one first copolymerizableα,β-ethylenically unsaturated monomer containing at least one hydroxylgroup. Component (a) is present in an amount of from 2.0 to 25.0 weightpercent, based on the total amount of copolymerizable monomers. Apreferred amount is from 3.0 to 15.0 weight percent, and a morepreferred amount is from 4.0 to 10.0 weight percent, all based on thetotal amount of monomers.

Preferred examples of hydroxyl containing monomers are, but are notlimited to, 2-hydroxyethyl (meth)-acrylate, 4-hydroxybutyl(meth)acrylate and hydroxypropyl (meth)-acrylate. A more preferredmonomer in accordance with the present invention is 2-hydroxy-ethylacrylate. The term "(meth)acrylate" as used herein denotes eithermethacrylate or acrylate.

Component (b)

Component (b) is a second copolymerizable α-β ethylenically unsaturatedmonomer which contains no hydroxyl groups, present in an amount of from75.0 to 98.0 weight percent, based on the total amount ofcopolymerizable monomers. Preferably, component (b) contains:

Component (i). Component (i) is preferably an α,β-ethylenicallyunsaturated monomer which may be represented by the general formula:

    CH.sub.2 =C(R.sub.1)COOR.sub.2

where R₁ is hydrogen or a C₁ -C₃ alkyl group, and R₂ is a C₁ -C₂₀ alkylgroup, phenyl, benzyl, C₁ -C₄ alkoxy-(C₁ -C₄) alkyl, cyclopentyl,hydroxy-(C₁ -C₄) -alkyl, cyclohexyl, furyl, C₁ -C₄ alkyl furyl,tetrahydrofuryl, C₁ -C₄ alkyl tetrahydrofuryl and combinations of thesemonomers thereof. Combinations of monomers where R₁ is hydrogen andmonomers wherein R₁ is an alkyl group may be used to modify the glasstransition temperature of the vinyl polymer. Preferred examples ofuseful monomers are, but are not limited to, C₁ -C₁₈ alkyl(meth)acrylates such as, methyl (meth)acrylate, ethyl (meth)acrylate,propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate,isobutyl (meth)acrylate, hexyl (meth)acrylate, isooctyl (meth)acrylate,isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate,phenoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, benzyl(meth)acrylate, ethoxyethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,cyclopentyl (meth)acrylate and isobornyl (meth)acrylate, as well ascombinations of those monomers. The term "alkyl" is used to denotestraight chain or branched alkyl groups.

A combination of these monomers may be used in order to achieve anappropriate Tg for the resulting vinyl polymer (A). Preferred monomersare butyl acrylate and methyl methacrylate. Component (i) may be presentin the vinyl polymer (A) in an amount of from 40.0 to 98.0 weightpercent, based on the total amount of monomers. However, a preferredamount is of from 50.0 to 98.0 weight percent and a more preferredamount is 70.0 to 98.0 weight percent, based on the total amount ofmonomers.

Component (ii). Optionally, component (b) may contain up to 40 weightpercent of a styrenic monomer, based on the total amount of monomers.The term styrenic monomer denotes styrene, or a substituted styrene suchas C₁ -C₆ alkyl ring-substituted styrene, C₁ -C₃ alkyl α-substitutedstyrene or a combination of ring and α-alkyl substituted styrene.Preferred styrenic copolymerizable monomers include styrene, p-methylstyrene, m-methyl styrene, o-methyl styrene, p-butyl styrene, α-methylstyrene and combinations thereof. More preferred are styrene, p-methylstyrene, m-methyl styrene, and α-methyl styrene. A preferred amount ofthe styrenic monomer is from 3.0 to about 25.0 weight percent. A morepreferred amount of styrenic monomer is from 4.0 to about 15.0 weightpercent, based on the total amount of monomers.

Component (iii). Optionally, component (b) may contain up to 10.0 weightpercent of (meth)acrylamide based on the total amount of monomers. Apreferred amount of component (iii) is up to 7.0 weight percent; a morepreferred amount is up to 4.0 weight percent, based on the total amountof monomers.

Component (iv). Optionally component (b) may contain up to 20.0 weightpercent, based on the total amount of monomers, of (meth)acrylonitrile.A preferred amount of component (iv) is 1.0 to 10.0 weight percent. Amore preferred amount of component (iv) is 2.0 to 6.0 weight percent,based on the total amount of monomers.

Component (v). Optionally, component (b) may contain an additionalcopolymerizable monomer in an amount of up to 20.0 weight percent, basedon the total amount of monomers. Such monomers may be selected from acidfunctional monomers, such as (meth)acrylic acid, crotonic acid, itaconicacid, maleic acid, fumaric acid, 2-acrylamido-2-methyl-1-propanesulfonicacid; sodium or potassium salts of the above acids; anhydrides of theabove acids; vinyl esters, such as vinyl acetate, vinyl propionate,vinyl 2-ethyl-hexanoate, vinyl neononanoate vinyl neodecanoate and vinylformate; castor oil; and copolymerizable monoglyceride, diglyceride andtriglyceride. Preferred monomers include monoglyceride, diglyceride andtriglyceride.

Component (vi). Optionally, component (b) may contain up to 2 weightpercent, based on the total amount of copolymerizable monomers, of acopolymerizable crosslinkable monomer. Useful crosslinkable monomers maybe selected from trimethylolpropane; tri(meth)acrylate; 1,6-hexanedioldi(meth)acrylate; allyl (meth)acrylate; divinyl benzene and the like. Ina preferred composition, a copolymerizable crosslinkable monomer isadded in an amount of up to 2 weight percent based on the total amountof copolymerizable monomers.

Vinyl polymer component (A), in accordance with the present invention,may be prepared as a solution or as a dispersion. In the case of asolution it is possible to utilize any solvent in which the monomers andthe ultimate vinyl polymer are soluble. Such solvents include water,acetone, methylethyl-ketone, ethylacetate, various alcohols and mixturesthereof

In a preferred embodiment an aqueous dispersion of vinyl polymercomponent (A) is formed. In accordance with this embodiment, aconventional surfactant or combination of surfactants can be used suchas anionic surfactants including, but not limited to, a fatty acid,alkali or ammonium alkylsulfate, alkylsulfonate, alkylarylsulfate,sulfated polyethoxylated alkyl phenol, sulfosuccinate, alkali orammonium alkylphosphate; or non-ionic surfactants, such as polyoxylatedfatty alcohol, polyethoxylated alkyl phenol, polyethoxylated fatty acid.Surfactants may be used in an amount up to 6.0 weight percent, based onthe total weight of the monomers. Preferred surfactants are sodiumdodecyl benzene sulfonate, sodium dodecyl sulfate or a diester of sodiumsulfosuccinic acid such as dioctylsulfosuccinate

Typical emulsion initiators may be used in accordance with known aqueousdispersion polymerization procedures. Such initiators include peroxygencompounds such as hydrogen peroxide; sodium, potassium or ammoniumpersulfate; t-butyl hydroperoxide; cumene hydroperoxide; laurylperoxide; benzoyl peroxide or persulfate compounds. A preferred amountof an initiator, in accordance with the present invention, is between0.05 and 1.5 weight percent, based on the total weight of the monomers.In addition, redox initiators may be used including, but not limited to,combinations of peroxygen compounds with sodium formaldehydesulfoxylate, isoascorbic acid, or divalent iron salts. The preferredamount of redox initiator is 0.02-1.5 weight percent, based on the totalweight of the monomer. The term "dispersion polymerization" is used todenote suspension or emulsion polymerization.

Emulsion polymerization is a more preferred embodiment. The reactiontemperature of an emulsion polymerization process is determined by thetype of initiator. Accordingly, the reaction temperature may range fromabout 20° C. to 90° C.; with a preferred reaction temperature beingbetween 60° C. and 85° C. In addition, a chain transfer agent may beused to regulate the molecular weight of the vinyl polymer. Examples ofchain transfer agents include, but are not limited to, mercaptans suchas dodecylmercaptan, t-butyl mercaptan, 2-ethylhexyl-3-mercaptopropionate; and haloalkyl compounds such as carbon tetrabromide andbromodichloromethane, as well as mixtures thereof.

Further, a wet adhesion promoting comonomer may be added to the emulsionpolymerization process. Examples of wet adhesion promoting monomersinclude t-butyl-aminoethyl methacrylate, dimethylaminoethylmethacrylate, diethylaminoethyl methacrylate, N,N-di-methylaminopropylmethacrylate, 2-t-butylaminoethyl methacrylate, N,N-dimethylaminoethylacrylate, and N-(2-methacryloxy-ethyl) ethylene urea.

A batch process or a semi-continuous process may also be used to formthe vinyl polymer component (A). A semi-continuous process representsanother preferred embodiment. In a preferred semi-continuous process,1.0 to 5.0 weight percent of a mixture of one or more monomers, fromcomponents (a) and (b), based on the total amount of monomers, isintroduced into the polymerization vessel together with a polymerizationinitiator and, optionally, a surfactant. Subsequently, the temperatureis raised to the reaction temperature and polymerization is initiated toproduce a seed. The remainder of the mixture of monomers along with apolymerization initiator may then be incrementally added to the aqueousdispersion of the seed and polymerized to produce an aqueous vinylpolymer. It is desirable to have less than 100 parts per million (ppm)of unsaturated monomers in the final product and preferably less than 50ppm unsaturated monomer (s). The aqueous dispersion thus produced can beprepared with a total solids content of from about 20% to about 65%. Itis preferred, for safety reasons, that the initiator not be mixed withthe monomers but added separately, although concurrently.

In a preferred embodiment of a semi-continuous process, a sequentialaddition of at least two monomer mixtures, differing in glass transitiontemperatures (Tg), is used. The term glass transition temperature of amonomer mixture means the Tg of a polymer derived from thepolymerization of the monomer mixture. The Tg of the vinyl polymer maybe adjusted depending on the requirement of the final use of the polymercomposition. For example, for a woven binder substrate the vinyl polymermay preferably have a Tg of from -50° to 15° C. A preferred Tg isbetween -35° to 0° C, and a more preferred Tg is between -30° to -10° C.However, a preferred Tg for a non-woven binder substrate is from -30° to40° C., with -15° to 20° C. being a more preferred Tg.

The vinyl polymer of the present invention preferably has a weightaverage molecular weight (Mw) from 50,000 to 8,000,000; more preferablyfrom 100,000 to 2,000,000; a most preferred Mw is 200,000 to 1,000,000,as measured by gel permeation chromatography (GPC).

In a preferred embodiment, where the vinyl polymer is in the form of adispersion, the particle size of the dispersion may be from 50 to 600nm. A preferred particle size for the dispersion is between 100 and 500nm; and a more preferred particle size is 160 to 350 nm. The polymerparticles generally have a spherical shape. In a preferred embodiment,the spherical polymer particles have a core portion and a shell portionor gradient structure. The core/shell polymer particles may also beprepared in multi-lobe forms, a peanut shell, an acorn form, a raspberryform or any other form as is known in the art.

COMPONENT (B)--Crosslinker

In the self-crosslinking polymer composition in accordance with thepresent invention, a crosslinker component is used in an amount of 0.1to 15 weight percent, based on the total amount of vinyl polymercomponent (A). A preferred amount of a crosslinker is from 1.0 to about6.0 weight percent; and a more preferred amount is of from 2.0 to about4.0%, based on the total amount of component (A). A preferredcrosslinker is a dialdehyde having the general formula CHO(CH₂)_(n) CHO,wherein n is an integer of 1 to 8. In addition, cyclic compounds such asdialdehydes are furaldehyde; 2,5-dialkoxy-2,5-dihydrofuran;2,5-dialkoxytetrahydrofuran; 3,4-dihydro-2-ethoxy-2H-pyran may also beused as component (B). Further, aldehyde-alcohols and equivalents suchas 2,3-dihydrofuran; 3,4-dihydro-2H-pyran may also be used as component(B). In addition formaldehyde or formaldehyde-melamine resins may beused as component (B).

More preferred crosslinkers are glyoxals, either free or blocked.Suitable blocked glyoxal resins which may be used are described in U.S.Pat. No. 4,695,606, incorporated herein by reference. However, the morepreferred form of glyoxal is free glyoxal. Glyoxal may be added duringthe polymerization of the monomers for component (A) above or after thepolymerization is complete.

Although applicants do not wish to be bound by any theories, it isbelieved that glyoxal does not enter into an irreversible reaction withthe vinyl polymer or any of the monomers in the presence of water.Glyoxal may however enter into reversible combinations with alcohols viathe formation of an acetal or with water to form hydrates. Glyoxal mayalso crosslink with hydroxyl as well as amide pendant functionalitiespresent on the vinyl polymer backbone, in addition to self crosslinking.Thus, the amount of glyoxal required in accordance with the presentinvention will depend on the amount of the combined hydroxyl and amidependant functionality on the polymer backbone as well as the desiredproperties.

Alternatively, the amount of glyoxal can be expressed as a ratioobtained by dividing the moles of glyoxal by the total number of molesof hydroxyl and amide moieties on the polymer backbone. The amount ofglyoxal so expressed may vary from 0.02 to 4.0. Preferably the amount ofglyoxal may vary from 0.1 to 2.5, and most preferably from 0.2 to 1.0.

In a preferred embodiment, glyoxal is used as a 40 weight percentaqueous solution. However, glyoxal may be used in any form, such as apure crystalline form. In addition glyoxal may be in the form of adimer, trimer or polymer. Generally, a monomeric glyoxal can reversiblybe formed from the above forms. Thus, any of the above forms of glyoxalcan be used as a source of monomeric glyoxal in accordance with thepresent invention. The above forms of glyoxal are discussed in U.S. Pat.No. 4,191,643, incorporated herein by reference.

In a preferred embodiment glyoxal is used in combination with diols suchas ethylene glycol, 1,6-hexanediol, diethylene glycol, propylene glycol,neopentyl glycol, 1,4-cyclohexane dimethanol, 1,3-cyclohexanedimethanol, glycerin, pentaerythritol, sugar, polyvinyl alcohol;carbamates, such as N,N-bis(2-hydroxyethyl)-2-hydroxyethylcarbamate;mono-, di-, or tri-glycerides with a hydroxyl value of at least 200 mgKOH per gram of the vinyl polymer; urea and substituted urea; castoroil; or an amine-alcohol. The amount of the additive, other thanglyoxal, may range from 10 mol percent to 500 mol percent based on theamount of glyoxal. A more preferred amount is 50 mol percent to 200 molpercent based on the amount of glyoxal.

COMPONENT (C)--Additive

Optionally, an additive component may be included as component (C) in anamount up to 2.0 weight percent, based on the amount of component (A).Such additives include fillers, fire retardants, foaming agents, oils,plasticizers, opacifiers, thickeners, optical brighteners, surfaceactive agents, catalysts, biocides, or other ingredients to providedesired end-use properties.

Suitable catalysts for accelerating the rate of reaction of Component(A) with Component (B) include, for example, inorganic and organic saltsof magnesium and aluminum; oxalic acid; citric acid; and aluminumnitrate.

In a preferred embodiment, additive component (C) is a foaming agentselected from monoglyceride, diglyceride and triglyceride. Monoglycerideis a preferred foaming agent for textile foam finishing applicationssuch as backcoating.

COMPONENT (D)--Solvent

The remainder of the self-crosslinking polymer composition is a solventcomponent. Useful solvents may be selected from water, acetone,methylethyl ketone, cellosolve acetate, alcohol, and mixtures thereof.Water is a preferred solvent; however, combinations of water and othersolvents may also be used.

A desired property of the present invention is that self-crosslinkingpolymer compositions comprising components (A), (B), (C) and (D) asdescribed above, are stable for prolonged periods during storage, yetcrosslink when applied to a substrate. Thus, the present composition isstable as a "one-package" system. The term "one-package" system, as usedherein, denotes that the reactive components of the composition, thehydroxyl containing vinyl polymer, component (A), and the crosslinker,component (B), are packaged together in the same container; as opposedto a "two-package" system where the crosslinkable polymer is in aseparate package from the crosslinking agent.

The "one-package" system of the present invention is "storage stable" atambient temperatures, meaning the self-crosslinking polymer compositionremains remains substantially uncrosslinked during storage overprolonged periods of time, up to about one year. At elevatedtemperatures, such as at 50° C., the self-crosslinking polymercompositions are stable for up to about four weeks.

Although applicants do not wish to be bound by any theories, it isbelieved that the storage stability of the crosslinker component (B) isimportant in the presence of an excess of water. It is believed that thecrosslinker, especially when glyoxal is used as crosslinker, exists as ahydrated moiety such as 1,1,2,2-tetrahydroxy ethane.

Commonly used commercial crosslinking systems typically employ specialtechniques to prevent premature crosslinking, such as the two-packagesystem described above. These systems require the combination of thecrosslinkable polymer with a crosslinker or catalyst immediately beforeuse. Although such technology is widely used and gives good results, theingredients have to be accurately measured and thoroughly blendedimmediately before application of the mixture. Another way to preventpremature self-crosslinking is to use an acid-catalyzed crosslinkingsystem which is neutralized with ammonia to a pH of about 8. Upondrying, ammonia is liberated, the system becomes acidic and theacid-catalyzed crosslinking reaction can occur. However, the evolutionof ammonia in the atmosphere during application of the coating presentsenvironmental and worker exposure concerns.

The self-crosslinking polymer compositions of the present invention areable to self-crosslink without the use of toxic reagents such asformaldehyde. This is particularly important with recent legislationaddressing environmental concerns in some states requiring control ofemission and worker exposure to volatile toxic materials.

Further, the self-crosslinking polymer compositions of the presentinvention crosslink without any added catalyst or heat. Films formedfrom polymers of the present invention and dried at ambient conditions,have substantially the same tensile properties as commercial polymerscured at elevated temperatures, such as 120° C. The low curingtemperature of the self-crosslinking polymer compositions of the presentinvention enable the use of these polymers in backcoating formulationsused on heat sensitive materials such as polypropylene, which melt atnormal thermal crosslinking temperatures used for curing commerciallybackcoating materials (greater than 120° C.). The low curing temperaturealso reduces curing time and increases production speeds in commercialoperations. Optionally, catalysts or elevated temperature may beemployed to accelerate or increase the extent of crosslinking ifdesired.

Further, the present self-crosslinking polymer compositions providepolymers with good distortion resistance and dimensional stability whilemaintaining flexibility.

In a preferred embodiment of the present invention, a backcoating orbinder formulation is formed by blending: vinyl polymer component (A) asdescribed above, present in an amount of from 10 to 65 weight percent,based on the total amount of the backcoating formulation; a crosslinkercomponent (B) as described above, present in an amount of from 0.1 to15.0 weight percent, based on the total amount of component (A); and anadditive component (C), as described above, present in an amount of upto 2.0 weight percent, based on the total amount of component (A). Thebackcoating or binder formulation further contains an associativethickener component (E), present in an amount of from 0.5 to 10.0 weightpercent, based on the total amount of the backcoating formulation;optionally, a surfactant component(F), present in an amount up to 10.0weight percent based on the total amount of the backcoating formulation;optionally, a plasticizer component (G), present in an amount up to 10.0weight percent, based on the total amount of the backcoatingformulation; and optionally, a filler component (H), present in anamount up to 25 weight percent based on the total amount of components(A), (B), (C), (E), (F) and (G). Again, the remainder of the backcoatingformulation is a solvent component (D).

Associative thickeners useful as component (E) are described in thetreatise: "Handbook of Coatings and Additives" Volume 2, J. Calb Editor,"Associative Thickeners", E. J. Schaller and P. R. Sperry, MarcelDekker, Inc., New York, 1992. Additionally, U.S. Pat. No. 4,722,962,incorporated herein by reference, describes associative thickenersuseful in the practice of the present invention. Such associativethickeners include ACRYSOL RM-825 available from Cytec Chemical Company.Commercial alkali-swellable thickeners commonly used for theseapplications achieve optimal viscosity increase at a pH of 9.0. However,glyoxal, a preferred crosslinker component (B) of the present invention,is unstable at that pH. Applicants have discovered that non-ionicassociative thickeners are preferred as component (E) when used incombination with glyoxal at a preferred pH of less than 8.0.

Specific examples of surfactants useful as optional component (F) may befound in the treatise: "McCutcheon's Emulsifiers and Surfactants", M.C.Publishing Co., Greenrock, N.J.,1993.

In addition, a plasticizer, optional component (G), may be added to thebackcoating formulations. Examples of useful plasticizers include, butare not limited to, oil, adipic esters, phthalate esters, isobutyrateesters, terephthalate esters, epoxidized butyl esters or fatty acids,epoxidized vegetable oils and polymeric plasticizers. More preferredplasticizers in accordance with the present invention are, vegetableoil, di-2-ethylhexyladipate or dioctyladipate (DOA),di-2-ethylhexylphthalate or dioctylphthalate (DOP), di-2-ethylhexylterephthalate (DOTP), dicyclohexylphthalate, diisononyladipate,diisononylphthalate, n-butylbenzylphthalate, 1,3-butylene glycol/adipicacid polyester, dialkyl adipate, dialkyl phthalate derivatives where thealkyl group is a C₁ -C₁₂ alkyl group, preferably a C₇, C₉ or C₁₂ alkylgroup, di-n-hexylazelate, diphenylphthalate, tricresol phosphate, benzylbenzoate, dibutyl phosphate, tributyl phosphate, tributoxyethylphosphate, triphenyl phosphate, butyl acetyl ricinoleate, glycerolacetyl ricinoleate, dibutyl phthalate, diethyl phthalate, dioctylphthalate, dimethoxyethyl phthalate, diisobutyl phthalate, diamylphthalate, dibutyl glycolate, butyl stearate, triethyl citrate, tributylcitrate, tributyl acetyl citrate, 2-hexyltriethylacetyl citrate, dibutyltartarate, camphore, epoxidized butyl esters of linseed oil fatty acids,epoxidized linseed oil, epoxidized soya oil, propylene glycol adipate,2,2,4-trimethyl-1,3-pentane-diol diisobutyrate, methylabietate, cumylacetate, dibutoxyethyl adipate, di-n-hexylazalate,glyceryl-tri-benzerate, tri-n-butylcitrate, dioctyl-fumarate,tri-isonyltrimellitate, dioctylisophthalate, butyloleate, chlorinatedparafin, tricresylphosphate or dibutyl-sebacate.

Optionally, a filler component (H) may be added to the backcoating orbinder formulations. Useful fillers may be selected from finely dividedclays, silicates, alumino-silicates and other finely divided materials.

Substrates useful in the practice of the present invention may be wovenor non-woven substrates. Preferred substrates are non-woven fabricsubstrates such as those composed of fibers of glass, quartz, graphite,KEVLAR, polyester, nylon, polypropylene, polyethylene, acetate, cotton,cellulose or blends of these fibers.

Backcoating or binder formulations of the present invention may beapplied using methods known in the art such as padding or impregnating;coating or foam finishing; and other known application methods.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended Claims, theinvention may be practiced otherwise than as specifically describedherein.

EXAMPLES Example 1 Latex Synthesis

The reaction was run in a 4-L jacketed kettle topped with a four-neckclosure. Agitation was with two four-blade propellers. The reactiontemperature was 80° C. The reactor was charged with 514 g of water, 1.4g of anhydrous sodium carbonate, 3.4 g of sodium dodecyl benzenesulfonate (SDBS). An emulsion was made with 901 g of water, 2 g ofsodium carbonate, 6.8 g of SDBS, 969 g of butyl acrylate, 595 g ofstyrene and 136 g of 2-hydroxyethyl acrylate (HEA). To the reactor wasadded 78 g of the emulsion followed by a solution of 3.5 g of sodiumpersulfate in 67 g of water. After 10 minutes, the emulsion was fed tothe reactor over three hours. After 30 minutes, a solution of 5 g ofsodium persulfate in 120 g of water was added over 90 minutes. Thereaction temperature of 80° C. was maintained for one hour after the endof the addition of the emulsion. The reaction mixture was cooled to 60°C. A chaser was then added to reduce the residual monomers, as follows:4.0 g of 0.5% aqueous ferrous sulfate solution, was added to the reactorall at once followed by 4 g of 70% t-butylhydroperoxide in 120 g ofwater; a solution of 4 g of sodium metabisulfite, 1 g of sodiumhydroxide and 120 g of water was added over 90 minutes. The product hada particle size of 119 nm, a pH of 6.5, and 45.3% solids.

Example 2 Backcoating Latex Synthesis

The reactor, as described in Example 1, was charged with 250 g of water,0.78 g of sodium carbonate and 256 g of the latex of Example 1. Afterheating to 80° C., a mixture of 3.2 g of sodium persulfate in 87 g ofwater was added. After 10 minutes, 91 g of a 40% mixture of glyoxal inwater was added over 150 minutes. At the same time, the emulsion feed,also lasting 150 minutes, was started. The emulsion consisted of 883 gof water, 9 g of SDBS, 1365 g of butyl acrylate, 309 g of styrene and146 g of HEA. One half hour after the emulsion feed was started, acatalyst solution consisting of 5.9 g of sodium persulfate and 156 g ofwater was started, and lasted 90 minutes. Heating was continued at 80°C. for one hour after the end of the emulsion. Residual monomers werereduced with the iron/peroxide/metabisulfite combination describedabove. The product had a particle size of 320 nm, a pH of 4.2, 51.4%solids, a viscosity of 90 cps, measured with a Brookfield viscometer, #2spindle, at 60 rpm, and Tg -20.7° C.

To 3455 g of this latex was added 44.4 g of a 40% solution of glyoxal inwater. This material and a styrene/acrylic control latex, commonly usedin the textile industry in this type of application, were formulated, asdescribed in Table I, and applied to fabric at the rate of 2.5 ouncesper square yard dry add-on (91 grams per square meter). Both sampleswere cured for 4 minutes at 250° F. (121° C.) and evaluated.

The latex described in this example gave a backcoated fabric which wasstronger, with a seam strength of 86.7 pounds per linear inch (15.5kg/cm), than the control, at 84.5 pounds per linear inch (15.1 kg/cm).

                  TABLE I    ______________________________________    Evaluation of Example 1 Against    A Standard Control Formulation    ______________________________________    Backcoating Formulation    Material     Control      Present Invention    ______________________________________    Latex        Styrene/Acrylic                              Latex from Example 1    Catalyst     None         None    Water        Water        Water    Filler       sodioaluminum                              sodioaluminum silicate                 silicate    Soap         Soap         Fast Soap    Soap         Soap         None    Plasticizer  Oil          Oil    pH Adjustment                 Aq. Ammonia  None    Thickener    Alkali Soluble                              Associative Thickener                 (ASE)    ______________________________________    Q.C. Specifications    Parameters    Control  Present Invention    ______________________________________    % Solids      51.50    53.12    Weight/Gallon 8.70     8.70    (#/gal)    Viscosity (cps)                  7,790    2,640    pH            9.30     5.00    ______________________________________    Viscosity Stability    Control                 Present Invention    Builds   Stir-backs                      Day       Builds                                      Stir-backs    (cps)    (cps)    (cps)     (cps) (cps)    ______________________________________    --       7,790    Initial   --    2,640    8,320    7,920     1        2,440 2,280    8,100    7,780     3        --    --    7,800    --        7        2,200 --    8.040    --       14        2,160 --    7,600    --       21        2,040 --    7,760    7,240    28        2,000 2,000    ______________________________________    Evaluation of Coated Fabric    (2.5 osy* dry add-on, 4 min. @ 250 deg. (F.)    Parameter      Control Present Invention    ______________________________________    Softness of    Soft    Softer    "hand":    Subjective    Seam Strength: 84.5    86.7    #/linear in.    ______________________________________     *osy = ounces per square yard

Example 3

The apparatus was the same as used in Example 1. The reactor was chargedwith 904 g of water, 0.34 g of (75% sodium dioctyl sulfosuccinate in amixture of ethanol and water, available as AEROSOL OT surfactant fromCytec Chemical Company), 40 g of butyl acrylate and 7 g of styrene. Thereactor was heated to 80° C. and a solution of 4.9 g of sodiumpersulfate in 67 g of water was added. After 15 minutes, the catalystand monomer mixtures were begun simultaneously. The monomer mixture wasfed over 170 minutes and consisted of 1160 g of butyl acrylate, 88 g ofstyrene, 158 g of methyl methacrylate, 127 g of 2-hydroxyethyl acrylateand 2.5 g of AEROSOL OT surfactant. The catalyst mixture was fed over160 minutes and consisted of 192 g of water, 3 g of sodium dodecylbenzene sulfonate, 2 g of sodium bicarbonate and 3 g of sodiumpersulfate. The reaction mixture was held at 80° C. for 30 minutes andcooled to 60° C. A mixture of 2.6 g of 70% t-butylhydro-peroxide inwater and 58 g of water was added all at once, and a mixture of 3 g ofsodium metabisulfite, 80 g of water and 40 g of a 40% solution ofglyoxal in water was added over one hour. The mixture was cooled to roomtemperature and filtered through a 100 mesh screen.

The latex had a particle size of 245 nm in 0.01M NaCl, a pH of 2.8,53.05% solids, a viscosity of 118 cps, and Tg -25° C.

Example 4

A latex with the same composition as the one described in Example 3, butwithout glyoxal, was prepared. Various levels of glyoxal were then addedto portions of the latex. One percent glyoxal means one gram of pureglyoxal per 100 g of dry polymer. The tensile strength, gel fraction andswell ratio of thin (10 mil, 0.25 mm) films of the air-dried latex (nocatalyst, no heat above room temperature) were determined.

Gel fraction was determined by soaking an accurately weighed 10 mil(0.25 mm) film in acetone for at least 16 hours. The mixture wasfiltered through a 100 mesh screen. The weight of polymer retained onthe 100 mesh screen was determined after drying in a 120° C. oven for atleast four hours. The gel fraction is the weight of oven-dried polymerretained on the 100 mesh screen divided by the original dry weight. Theoriginal dry weight is defined as the actual weight of the sample minusthe weight of volatile matter. Volatile matter was determined by dryinga separate sample in a 120° C. oven for at least six hours.

Swell ratio was determined by soaking an accurately weighed 10 mil (0.25mm) film in acetone for at least 16 hours. The weight of the acetone-wetpolymer was determined. The swell ratio is the weight of the polymerswollen with acetone divided by the original dry weight, as definedabove.

Tensile strength was determined according to ASTM D 882. The dry filmthickness was approximately 8-10 mils (0.20 to 0.25 mm). Samples wereair dried in the laboratory for a day, followed by at least two days ina constant temperature-humidity room held at 22° C. and 50% relativehumidity. The reported value is the average of ten. The results areshown below in Table II.

                  TABLE II    ______________________________________                      Tensile    Percent   Percent Strength    Gel   Swell    Glyoxal   Volatile                      kg/cm       Fraction                                        Ratio    ______________________________________    0         1.18    3.0*        0.35  --**    0.5       1.60    10.1        0.48  --**    1         2.11    18.3        0.71  14.3    2         3.04    38.7        0.86  6.9    3         4.12    39.2        0.89  5.3    4         5.13    52.4        0.90  4.4    5         6.41    61.8        0.91  4.0    ______________________________________     *This sample was weak and difficult to handle; only two measurements were     done as opposed to ten for the other samples.     **Could not be determined.

Example 5 Flexibility Measurements

Each sample was a 40×10 mm free film prepared from the latex of Example4 with 2% glyoxal, and from commercial latexes available from Rohm andHaas. Exactly 20 mm of the sample was allowed to dangle unsupported.After 22 hours, the angle of repose was calculated from measurements ofthe distance of the end of the sample from the vertical plane, and fromthe supporting horizontal surface. The angle of repose is defined as theangle formed by the vertical surface, the square horizontal edge and theend of the polymer sample. A low value indicates a soft, flexiblematerial. The data, shown in Table III below, demonstrates thestronger-yet-softer property of the polymer compositions of the presentinvention.

                  TABLE III    ______________________________________                Angle of              Tensile                Repose (from Thickness,                                      Strength,    Sample      the vertical)                             mm       kg/cm.sup.2 (psi)    ______________________________________    Latex of    11.3° 0.392    38.7 (551)    Example 3    with 2%    glyoxal    Rohm and Haas                14.5° 0.406    17.1 (243)    NW-1845 latex    ______________________________________

Example 6 A Formulated Backcoating Mixture

(a) Preparation of a crosslinking latex. A latex with the samecomposition as the one described in Example 3, but without glyoxal, wasprepared. Glyoxal, as a 40% solution in water, was added at the rate of3 g of pure glyoxal per 100 g of dry polymer weight. The latex was 52.2%solids.

(b) Preparation of a backcoating mixture: Sodium dodecyl sulfate (6 g)was dissolved in 100 g of water. To this was added, with moderatestirring, 190.5 g of the latex described in (a), 100 g of powderedsodium aluminum silicate, 25 g of soybean oil and 5.7 g of ACRYSOL®RM-825 thickener (available from Cytec Chemical Company).

(c) Foaming the mixture: The mixture described in (b) was blended with aheavy-duty KITCHENAID blender equipped with a wire whisk for twominutes. The resulting foam had a density of 0.13 grams per milliliter,and was stable for at least one hour.

(d) Viscosity stability of the backcoating mixture: In a manner similarto (b), a backcoating mixture was prepared from 100 g of water, 7 g ofsodium dodecyl sulfate, 190.5 g of the latex described in (a), 100 g ofpowdered sodium aluminum silicate, 25 g of soybean oil and 23.5 g ofACRYSOL® RM-825 thickener. This mixture was not foamed. The viscosity ofthe mixture was 5660 cps, measured with a Brookfield viscometer, #3spindle, at 12 rpm. After 34 days, the viscosity was 5780 cps.

Example 7

A mixture of 100 g of water, 4 g of MYVATEX TEXTURE LITE emulsifier(available Eastman Chemical Company), a mixture of glycerolmonostearate, propylene glycol monostearate, and sodium stearoyllactylate), 194 g of a latex (51.6% solids) with the same composition asthe latex of Example 1, 100 g of powdered sodium aluminum silicate and25 g of soybean oil was blended until homogenous and then foamed asdescribed in Example 6. The foam had a density of 0.24 g per milliliter.

Example 8

A copolymer latex consisting of 76% butyl acrylate, 14% methylmethacrylate, 2% styrene, 8% 2-hydroxyethyl acrylate was prepared by aprocedure similar to Example 3. The particle diameter was 319 nm and theglass transition temperature was -25° C. Glyoxal was added at the rateof 2 grams per 100 g of dry polymer. The tensile properties of a freefilm of the unformulated latex, never heated above room temperature, isshown in FIG. 1. Commercial latexes, from Rohm and Haas, NW-1845,uncured, and E-2780, heated at 120° C. for 2 minutes, were analyzed in asimilar fashion. FIG. 1 shows that the present invention provides astronger product with a higher modulus.

Example 9

Use of Crosslinking Latex as a Non-woven Binder

A fiberglass substrate, obtained from CEM Corporation, was cut to athickness of 0.35 mm, padded (impregnated) with the two latexesdescribed in Example 6 (a) above, dried overnight and then stored at 22°C. and 50% relative humidity for three days. The results are shown inTable IV below.

                  TABLE IV    ______________________________________                  Application    Description   Rate      Tensile Strength    ______________________________________    Untreated     0         6.5 kg/cm.sup.2    Latex with no 44.7 g/m.sup.2                             31 kg/cm.sup.2    glyoxal    Latex with 3% 41.8 g/m.sup.2                             70 kg/cm.sup.2    glyoxal    ______________________________________

What is claimed is:
 1. A self-crosslinking polymer composition comprising:(A) a vinyl polymer component present in an amount from 20.0 to 65.0 weight percent, based on the total amount of the polymer composition, said vinyl polymer comprising the polymerization product of:(a) at least one first, copolymerizable α,β-ethylenically unsaturated monomer containing at least one hydroxyl group, present in an amount from 2.0 to 25.0 weight percent based on the total amount of α,β-ethylenically unsaturated copolymerizable monomers; (b) a second copolymerizable α,β-ethylenically unsaturated monomer containing no hydroxyl groups, present in an amount from 75.0 to 98.0 weight percent, based on the total amount of α,β-ethylenically unsaturated copolymerizable monomers; said second monomer comprising:(i) 40.0 to 98.0 weight percent, based on the total amount of monomers, of a C₁ -C₈ alkyl (meth)acrylate, (ii) optionally, up to 40.0 weight percent, based on the total amount of monomers, of a styrenic monomer, (iii) optionally, up to 10.0 weight percent, based on the total amount of monomers, of (meth)acrylamide, (iv) optionally, up to 20.0 weight percent, based on the total amount of monomers, of (meth)acrylonitrile, (v) optionally, up to 20.0 weight percent, based on the total amount of monomers, of an additional copolymerizable monomer, and (vi) optionally, up to 2.0 weight percent, based on the total amount of monomers, of a copolymerizable crosslinkable monomer; (B) a free glyoxal crosslinker component present in an amount from 0.1 to 15.0 weight percent, based on the total amount of component (A); (C) optionally, an additive component present in an amount up to 2.0 weight percent, based on the total amount of component (A); and (D) a solvent component being the remainder of said polymer composition.
 2. The self-crosslinking polymer composition of claim 1, wherein component (a) is present in an amount of from 3.0 to 15.0 weight percent, based on the total amount of monomers.
 3. The self-crosslinking polymer composition of claim 1, wherein component (a) is selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and hydroxypropyl (meth)acrylate.
 4. The self-crosslinking polymer composition of claim 1, wherein component (i) is selected from the group consisting of butyl acrylate and methyl methacrylate.
 5. The self-crosslinking polymer composition of claim 1, wherein component (ii) is present in an amount of 3.0 to 25.0 weight percent, based on the total amount of copolymerizable monomers.
 6. The self-crosslinking polymer composition of claim 1, wherein component (ii) is selected from the group consisting of styrene, p-methyl styrene, m-methyl styrene, and α-methyl styrene.
 7. The self-crosslinking polymer composition of claim 1, wherein component (iii) is present in an amount of up to 10.0 weight percent, based on the total amount of copolymerizable monomers.
 8. The self-crosslinking polymer composition of claim 1, wherein component (iv) is present in an amount of from 1.0 to 10.0 weight percent, based on the total amount of monomers.
 9. The self-crosslinking polymer composition of claim 1, wherein component (v) is selected from the group consisting of acid functional monomers; salts of acid functional monomers; anhydrides of acid functional monomers; vinyl esters; castor oil; monoglyceride; diglyceride; and triglyceride.
 10. The self-crosslinking polymer composition of claim 1, wherein component (vi) is selected from the group consisting of trimethylol propane tri(meth)acrylate, 1,6-hexane diol di(meth)acrylate, allyl methacrylate and divinyl benzene.
 11. The self-crosslinking polymer composition of claim 1, wherein component (B) is present in an amount of from 1.0 to 6.0 weight percent, based on the total amount of vinyl polymer (A).
 12. The self-crosslinking polymer composition of claim 1, wherein component (D) is selected from the group consisting of water, acetone, methylethylketone, cellosolve acetate, alcohol, and mixtures thereof.
 13. A backcoating formulation, comprising:(A) a vinyl polymer component present in an amount from 10.0 to 65.0 weight percent, based on the total amount of said backcoating formulation, said vinyl polymer comprising polymerization product of(a) at least one first, copolymerizable α,β-ethylenically unsaturated monomer containing at least one hydroxyl group, present in an amount from 2.0 to 25.0 weight percent based on the total amount of α,β-ethylenically unsaturated copolymerizable monomers; (b) a second copolymerizable α,β-ethylenically unsaturated monomer containing no hydroxyl groups, present in an amount from 75.0 to 98.0 weight percent, based on the total amount of α,β-ethylenically unsaturated copolymerizable monomers; said second monomer comprising:(i) 40.0 to 98.0 weight percent, based on the total amount of monomers, of a C₁ -C,₈ alkyl (meth)acrylate, (ii) optionally, up to 40.0 weight percent, based on the total amount of monomers, of a styrenic monomer, (iii) optionally, up to 10.0 weight percent, based on the total amount of monomers, of (meth)acrylamide, (iv) optionally, up to 20.0 weight percent, based on the total amount of monomers, of (meth)acrylonitrile, (v) optionally, up to 20.0 weight percent, based on the total amount of monomers, of an additional copolymerizable monomer; and (vi) optionally, up to 2.0 weight percent, based on the total amount of monomers, of a copolymerizable crosslinkable monomer; (B) free glyoxal crosslinker component present in an amount from 0.1 to 15.0 weight percent, based on the total amount of component (A); (C) an additive component present in an amount up to 2.0 weight percent, based on the total amount of component (A); (D) the remainder of the formulation being a solvent; (E) an associative thickener component present in an amount from 0.5 to 10 weight percent, based on the total amount of the backcoating formulation; (F) optionally, a surfactant component present in an amount up to 10 weight percent, based on the total amount of the formulation of a surfactant; (G) optionally, a plasticizer component present in an amount up to 10.0 weight percent based on the total amount of the backcoating formulation; and (H) optionally, a filler component present in an amount up to 10.0 weight percent, based on the total amount of the backcoating formulation.
 14. The backcoating formulation of claim 13, wherein said formulation has a pH of less than 8.0 and, component (E) is a non-ionic associative thickener.
 15. The backcoating formulation of claim 13, wherein additive component (C) is selected from the group consisting of monoglyceride, diglyceride and triglyceride. 